Ive had hellroaring battery isolators before , which sense your truck ignition and open the link between camper and truck, but isolaters in general rob a little of the charge power your trying to use on the camper to run the isolater. Not sure if hellroaring is even made anymore , it was the best back in 06
I use a simple solinoid ahat can be picked up at any rv parts store, its the cheapest , about 20.00 , way to go . Charge power in terminal, and out terminals , and a smaller terminal that when hot is conected to it opens the solinoid and lets power run thru,you connect this to the ignition wire on the truck , on Dodge can be found in fuse box under hood. There are models with ground terminals and without.
Ignition on power runs to camper . Off it dosent
I would abandon the factory wire for hot unless its at least a #10, and run new #8 from one battery terminal thru a thermal breaker and to the solinoid then to the plug to 5th - camper
Or you could just find the hot 5th -camper wire and cut one in